1. Field of the Invention
The present invention relates to methods for the synthesis of substituted 1,1,1-triaryl-2,2,2-trifluoroethanes and to products resulting therefrom, as well as to derivatives derived from said products. The polymeric derivatives of said products meet or exceed the performance characteristics required for high temperature resins and composites in present or future aeronautic requirements.
The utility of polyimides as a class of polymers is well-known. Polyimides, because of their low cost, excellent thermo-oxidative stability, chemical stability, and commercial availability, are in a class by themselves. They exhibit widespread applications, such as for films, coatings, moldings, adhesives, binder solutions and matrix resins. Extensive review articles and books, such as in Heat-Resistant Polymers, J. P. Critchley, et al, chapter 5, on Polyimides, (Plenum Press, 1983) describe the many polyimides that have been prepared and indicate which compositions are successful commercial variants. In a class by themselves are the fluorinated containing 1,1,1,3,3,3-hexafluoroisopropylidene (6F) polyimides because of their superior thermal stability compared to non-fluorinated polyimides. The 6F containing polyimides have become the state-of-the-art in melt processable polyimides for moldings and matrix resin applications. This patent application is designed to show new synthetic routes for the new 1,1,1-triaryl-2,2,2-trifluoroethane (3F) containing monomers which will exhibit all the desirable melt fusible-melt processable characteristics of 6F containing monomers but in addition are more versatile than 6F containing monomers because of the potentials described to introduce a variety of functional groups for the modification of polymer properties. In addition, this disclosure claims a variety of methods to effect the functional group introduction, such as from during the initial monomer synthesis, to during a later step in the monomer synthesis, to performing functional group changes on the final polymer structure. The copending Lew (Ser. No. 924,470 pending) disclosure generally claims the polymerization to new 3F polyimides after the functional groups for modifying polymer properties are already within the monomer structure but is not limited to introduction of functional groups prior to polymerization. Changes in functional groups may be effected once a functional group already exists within a 3F containing polymer.
2. Description of the Prior Art
Presently, one method of meeting high temperature performance requirements has been through the use of commercially available thermo-oxidatively stable monomers/polymers based on a 2,2-diaryl-1,1,1,3,3,3-hexafluoroisopropylidene structure (6F). A 1,1,1-triaryl-2,2,2-trifluoroethane structure (3F) is also known. ##STR1##
The synthesis of dianhydrides and diamines based on similar 6F structures has been previously reported as follows and is described within examples in U.S. Pat. No. 3,310,573, which issued on Mar. 21, 1967. ##STR2##
The dianhydride of example IX of U.S. Pat. No. 3,310,573 is presently used in commercially available resin products (called NR 150 resins) available from E. I. duPont. The 6F dianhydride and 6F diamine monomers are also presently available in developmental quantities from American Hoechst. A similar 6F diamine with meta, rather than para, substitution has been recently synthesized, K. S. Y. Lau, et al., J. Polymer Science, 20, 2381-2393 (1982), and is also available from American Hoechst in developmental quantities. The synthesis of this diamine is summarized below. ##STR3##
The synthesis of similar diamines but based on a 3F structure through a different synthetic route has been reported using aniline with an anilinium hydrochloride catalyst, by W. D. Kray and R. W. Rosser, J. Org. Chem., 42, 1186-1189 (1977). ##STR4## However, a different synthetic route to 3F di- and tri-acids was also reported within this reference and U.S. Pat. No. 4,307,024 was issued to Kray, et al for that procedure. ##STR5## However, neither of the Kray, et al references describe the synthesis of a tetra substituted 3F structure required to prepare a new 3F dianhydride monomer. Nor do these references describe the requirement to use stoichiometric, rather than catalytic, amounts of CF.sub.3 SO.sub.3 H condensing agent based on equimolar or greater amounts of CF.sub.3 SO.sub.3 H with the aryl trifluoromethyl ketone.
The utility of the synthesis of 3F monomers over state-of-the-art 6F monomers is because the 3F phenyl ring is useful as a synthetic site. This utility creates 3F synthesis technology as the next generation of more synthetically versatile polymers compared to the state-of-the-art 6F polymers currently claimed for specialized applications such as solar cell coatings (U.S. Pat. No. 4,592,925) or radiation-resistant or radiation sensitive modified 6F monomers (U.S. Pat. No. 4,416,973). A further utility of 3F monomers over non-3F or 6F monomers/polymers is in the synthetic procedure to prepare 2,6-substituted and disubstituted 3F diamines for potential use as photoresists. This advances the technology of non-fluorinated photoresists described in J. Pfeifer and O. Rhode of Ciba-Geigy in "Direct Photoimaging of Fully Imidized Solvent Soluble Polyimides" in proceedings of 2nd International Conference on Polyimides, Apr. 30, 1985-Nov. 1, 1985 at Ellenville, New York.